Pundit is a tool that allows you to restrict certain parts of your Rails application to authorized users. It does this by providing you with certain helpers.
In this tutorial, you will build a blog that restricts parts such as creating, updating and deleting articles to authorized users only.
Getting Started
Start by generating a new Rails application.
rails new pundit-blog -T
The -T flag tells Rails to generate the new application without the default test suite. Running the command will generate your Rails application and install the default gems.
Go ahead and add the following gems to your Gemfile. You will be using bootstrap-sass for the layout of your application, and Devise will handle user authentication.
#Gemfile ... gem 'bootstrap-sass' gem 'devise'
Run the command to install the gem.
bundle install
Now rename app/assets/stylesheets/application.css to app/assets/stylesheets/application.scss. Add the following lines of code to import bootstrap.
#app/assets/stylesheets/application.scss ... @import 'bootstrap-sprockets'; @import 'bootstrap';
Create a partial named _navigation.html.erb to hold your navigation code; the partial should be located in app/views/layouts directory. Make the partial look like what I have below.
#app/views/layouts/_navigation.html.erb
<nav class="navbar navbar-inverse">
<div class="container">
<div class="navbar-header">
<%= link_to 'Pundit Blog', root_path, class: 'navbar-brand' %>
</div>
<div id="navbar">
<ul class="nav navbar-nav pull-right">
<li><% link_to 'Home', root_path %></li>
<ul class="nav navbar-nav pull-right">
<% if user_signed_in? %>
<li><%= current_user.email %></li>
<li><%= link_to 'Log out', destroy_user_session_path, method: :delete %></li>
<% else %>
<li><%= link_to 'Log In', new_user_session_path %></li>
<li><%= link_to 'Sign Up', new_user_registration_path %></li>
<% end %>
</ul>
</ul>
</div>
</nav>
For the navigation to be used, you need to render it in your application layout. Tweak your application layout to look like what I have below.
#app/views/layouts/application.html.erb
<!DOCTYPE html>
<html>
<head>
<title>Pundit-Blog</title>
<%= csrf_meta_tags %>
<%= stylesheet_link_tag 'application', media: 'all', 'data-turbolinks-track': 'reload' %>
<%= javascript_include_tag 'application', 'data-turbolinks-track': 'reload' %>
</head>
<body>
<%= render "layouts/navigation" %>
<div id="flash">
<% flash.each do |key, value| %>
<div class="flash <%= key %>"><%= value %></div>
<% end %>
</div>
<div class="container-fluid">
<%= yield %>
</div>
</body>
</html>
Generate the User Model
Run the command to install Devise.
rails generate devise:install
Now generate your User model.
rails generate devise User
Migrate your database.
rake db:migrate
Generate Article Resources
Run the command to generate your Article resources.
rails generate scaffold Articles title:string body:text
This will generate your ArticlesController and Article Model. It will also generate the views needed.
Now migrate your database by running:
rake db:migrate
Open up app/views/articles/_form.html.erb and make it look like what I have below.
#app/views/articles/_form.html.erb
<%= form_for(article) do |f| %>
<% if article.errors.any? %>
<div id="error_explanation">
<h2><%= pluralize(article.errors.count, "error") %> prohibited this article from being saved:</h2>
<ul>
<% article.errors.full_messages.each do |message| %>
<li><%= message %></li>
<% end %>
</ul>
</div>
<% end %>
<div class="field">
<%= f.label :title %>
<%= f.text_field :title %>
</div>
<div class="field">
<%= f.label :body %>
<%= f.text_area :body %>
</div>
<div class="actions">
<%= f.submit %>
</div>
<% end %>
For your index file, it should look like this.
#app/views/articles/index.html.erb
<table class="table table-bordered table-striped table-condensed table-hover">
<thead>
<tr>
<th>Title</th>
<th>Body</th>
<th colspan="3"></th>
</tr>
</thead>
<tbody>
<% @articles.each do |article| %>
<tr>
<td><%= article.title %></td>
<td><%= article.body %></td>
<td><%= link_to 'Show', article %></td>
<td><%= link_to 'Edit', edit_article_path(article) %></td>
<td><%= link_to 'Destroy', article, method: :delete, data: { confirm: 'Are you sure?' } %></td>
</tr>
<% end %>
</tbody>
</table>
<br>
<%= link_to 'New article', new_article_path %>
The above code arranges the articles on the index page into a table format to make it look presentable.
Open up your routes file and add the route for articles resources.
#config/routes.rb ... resources :articles root to: "articles#index"
Integrate Pundit
Add the Pundit gem to your Gemfile.
#Gemfile ... gem 'pundit'
Run the command to install.
bundle install
Integrate Pundit to your application by adding the following line to your ApplicationController.
#app/controllers/application_controller.rb ... include Pundit ...
Run Pundit's generator.
rails g pundit:install
This will generate an app/policies folder which contains a base class with policies. Each policy is a basic Ruby class.
This is how the base class policy looks.
#app/policies/application_policy.rb
class ApplicationPolicy
attr_reader :user, :record
def initialize(user, record)
@user = user
@record = record
end
def index?
false
end
def show?
scope.where(:id => record.id).exists?
end
def create?
false
end
def new?
create?
end
def update?
false
end
def edit?
update?
end
def destroy?
false
end
def scope
Pundit.policy_scope!(user, record.class)
end
class Scope
attr_reader :user, :scope
def initialize(user, scope)
@user = user
@scope = scope
end
def resolve
scope
end
end
end
Create the Article Policy
Now you need to write your own policy. For this tutorial, you want to allow only registered users to create new articles. In addition to that, only creators of an article should be able to edit and delete the article.
To achieve this, your article policy will look like this.
#app/policies/article_policy.rb
class ArticlePolicy < ApplicationPolicy
def index?
true
end
def create?
user.present?
end
def update?
return true if user.present? && user == article.user
end
def destroy?
return true if user.present? && user == article.user
end
private
def article
record
end
end
In the above, you are permitting everyone (registered and non-registered users) to see the index page. To create a new article, a user has to be registered. You use user.present? to find out if the user trying to perform the action is registered.
For updating and deleting, you want to make sure that only the user who created the article is able to perform these actions.
At this point, you need to establish a relationship between your Article and User model.
You do so by generating a new migration.
rails generate migration add_user_id_to_articles user:references
Next, migrate your database by running the command:
rake db:migrate
Open the User model and add the line that seals the relationship.
#app/models/user.rb ... has_many :articles
Your Article model should have this.
#app/models/article.rb ... belongs_to :user
Now you need to update your ArticlesController so it is in sync with what you have done so far.
#app/controllers/articles_controller.rb
class ArticlesController < ApplicationController
before_action :set_article, only: [:show, :edit, :update, :destroy]
# GET /articles
# GET /articles.json
def index
@articles = Article.all
authorize @articles
end
# GET /articles/1
# GET /articles/1.json
def show
end
# GET /articles/new
def new
@article = Article.new
authorize @article
end
# GET /articles/1/edit
def edit
end
# POST /articles
# POST /articles.json
def create
@article = Article.new(article_params)
@article.user = current_user
authorize @article
respond_to do |format|
if @article.save
format.html { redirect_to @article, notice: 'Article was successfully created.' }
format.json { render :show, status: :created, location: @article }
else
format.html { render :new }
format.json { render json: @article.errors, status: :unprocessable_entity }
end
end
end
# PATCH/PUT /articles/1
# PATCH/PUT /articles/1.json
def update
respond_to do |format|
if @article.update(article_params)
format.html { redirect_to @article, notice: 'Article was successfully updated.' }
format.json { render :show, status: :ok, location: @article }
else
format.html { render :edit }
format.json { render json: @article.errors, status: :unprocessable_entity }
end
end
end
# DELETE /articles/1
# DELETE /articles/1.json
def destroy
@article.destroy
respond_to do |format|
format.html { redirect_to articles_url, notice: 'Article was successfully destroyed.' }
format.json { head :no_content }
end
end
private
# Use callbacks to share common setup or constraints between actions.
def set_article
@article = Article.find(params[:id])
authorize @article
end
# Never trust parameters from the scary internet, only allow the white list through.
def article_params
params.require(:article).permit(:title, :body, :user_id)
end
end
At this point in your application, you have successfully implemented the policies that restrict certain parts of your application to selected users.
You want to add a standard error message that shows whenever a non-authorized user tries to access a restricted page. To do so, add the following to your ApplicationController.
#app/controllers/application_controller.rb
...
rescue_from Pundit::NotAuthorizedError, with: :user_not_authorized
private
def user_not_authorized
flash[:warning] = "You are not authorized to perform this action."
redirect_to(request.referrer || root_path)
end
This code simply renders a basic text that tells the user s/he is not authorized to perform the action.
Run:
$ rails server
To start your Rails server, point your browser to http://localhost:3000 to see what you have.
Conclusion
In this tutorial, you learned how to work with both Devise and Pundit. You were able to create policies that allowed only authorized users to view certain parts of the application. You also created a basic error text that shows when a non-authorized user tries to access a restricted part of the application.
You can learn more about Pundit by checking the GitHub page.
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